Changelog

Every released version, newest first.

Downloads for each release are on the GitHub releases page, and the install instructions are in Installation.

0.3.1 — 2026-09-18

Fixed

maxon run and a path-less maxon build refused to run anything on a host whose home directory cannot be written, rather than using the next cache directory in the list. A container started with a numeric user that has no account entry is the common way to meet this: the home directory is the filesystem root, nothing can be created under it, and every program was refused. A run now keeps to the same order as before and takes the first directory it can actually create.
The refusal, when no directory at all can be created, names every variable the host consults instead of quoting whichever one it stopped on.
The Docker images could not run a program as any user without an account entry, which is both variants’ documented use. They name a writable temporary directory now.

Changed

maxon cache marks as in use the directory a run will actually fill, and where no directory can be created it says so instead of marking nothing. Reporting the cache now creates that directory if it is absent, which is what the next run would have done.

0.3.0 — 2026-09-17

Added

maxon cache, which reports what the run cache holds on this host and which root the next run will fill, and maxon cache clear, which empties it. The cache moved out of the host’s scratch area, where a temporary-file reaper could sweep it mid-session, into <home>/.maxon/cache beside the compiler an install puts there.
Directory.delete, which removes an empty directory and tells notFound, notEmpty and deleteFailed apart.
Runtime.processorCount(), the number of processors the scheduler runs green threads on.
Json.quote, the JSON string escape three places in the standard library and the tooling each had a private copy of.
Two worked examples — maxgrep, a parallel grep, and msort, a parallel merge sort — each beside a tour that reads it.
A complete reference on maxon.dev: the language, the standard library, the command line and every diagnostic, generated from the sources the compiler itself is checked against.

Changed

The compiler lexes and parses over a worker pool rather than one thread. On its own source that stage spent 7.3 seconds on one processor of sixteen before the change.
A let argument to a service message is LENT rather than moved. The sender keeps its reference and goes on reading the value after the send, where the only way to keep reading one was to clone it; var arguments, temporaries and literals still move. A lent graph is read-only while the service can see it, and a write reaching it through another path is refused (E3160).
A value held at an interface type crosses a message — as a spawn argument, a message parameter or a reply.
A record a callee builds crosses a service boundary as freshly owned, whether it is returned from a local it filled or produced by a qualified, static or try-guarded call. The proof followed one hop and recognised one spelling before.
A struct-literal field initializer and a field assignment widen a concrete value into an interface-typed field, as a call argument already did.
A closure written at an argument whose parameter is declared with a function type takes its parameter types from that declaration, so a comparator passed to sort needs no annotations. That offer was made at one position only.
match accepts or-arms over a combined error — an awaited reply’s own errors merged with ServiceError.stopped, or a block try’s handler over several error types. A handler that binds a combined error carrying a boxed member must match it exactly once (E3161), which the release model had left unsound in both directions.
A callee that writes a FIELD of its parameter earns E3019 at the call. bump(a) with bump doing b.n = 99 compiled and wrote through a binding the caller had declared immutable; a method writing its own receiver stays legal, and so does a callee that only calls such a method.
A Vector held inside an element type no longer makes the containing Array uncloneable.
HttpClient refuses any scheme but http before it connects, rather than sending an https URL as plaintext to port 80.
A missing executable is executableNotFound on every operating system, and a failed spawn names which step failed — stream setup, working directory or launch. A working directory that does not exist was silently ignored on Linux.
A build.maxon manifest’s debug_info is honoured; it was written and read by nothing. A manifest build now takes the tree lock and applies the same build-option refusals a command-line build does, and malformed manifest fields — a non-string version or source, a define with no =, a non-array defines — are refused rather than silently dropped.
maxon build with no path reports one line about its build runner instead of that runner’s own compile chatter.

Fixed

A Map or Set under insert-and-remove churn degraded until every lookup probed the whole table, because a removed slot counted toward nothing. A thousand rounds over one map and one set took 8.07 seconds; four thousand now take 87 milliseconds.
FilePath.parent() of a path directly under a root answered an empty or drive-relative path instead of the root, so a walk upwards never stopped at the top — it began asking the filesystem about the working directory and getting plausible answers back. The parent of a root now throws noParent.
A spawn or a send could stop the program reporting a second owner for a value that had one: the temporaries its arguments built were released after the ownership walk rather than before, and a reply’s walk ran before the handler had released what it held.
Reading a promise through an array cursor crashed the compiler when the reply carried a companion error type, and a program awaiting promises read that way stopped before its results were in.
SharedSegment.readWord, writeWord and copyOut read and wrote past the end of the segment instead of throwing outOfBounds.
On Windows, maxon upgrade and the one-line installer could fail when the calling shell’s module path hid the host’s own PowerShell modules.

Removed

optimize in a build.maxon manifest, which named optimization levels that do not exist.

0.2.2 — 2026-09-16

Added

MAXON_PREEMPT=off, which stops the scheduler taking a processor back from the green thread holding it, for a program whose result depends on a thread running uninterrupted. Unset or on preempts as before; any other value stops the program before main runs.

Changed

maxon build, and maxon with no arguments, open with the version line and a warning that Maxon is an early preview whose language, standard library and tools may change incompatibly between releases.
A build reports how long the compile took, and no longer prints a line naming the executable format it wrote.
The one-line installers make maxon work in the terminal that ran them rather than only in the next one. On macOS and Linux, an install whose PATH already holds a writable ~/.local/bin or ~/bin links the compiler there and edits no shell profile.

Fixed

A StreamingSubprocess handle kept after its child was released could drive the next child the runtime started in the same slot — waiting on it, reading its output, writing to its input. A copied StreamingSubprocess value reached this on its own, because each copy tracked release separately. A released handle is refused now.
The sixty-fifth runDetached in a program’s life failed, because a detached child never gave its runtime slot back.
Releasing a StreamingSubprocess while another green thread collected it left the collector reading a slot holding no child, and could corrupt the poll records of unrelated sockets and pipes. Two green threads collecting one handle stopped with the error for two readers on one socket. Each of the three is a named stop of its own now.
A socket closed and reopened while an operation was parked on it could take the previous socket’s timeout, or wake a green thread that no longer owned it.
Connecting to, or binding, an address written as a dotted quad parked the green thread for a name resolution that never ran.
On Windows, a socket send or receive cancelled by its deadline after the kernel had already moved part of the buffer reported a timeout and no count, so a retried send went out twice and received bytes were consumed unseen. It reports what it moved, and the deadline is reported by the next call.
On Windows, opening, connecting to and closing a socket counted as blocking kernel calls, so the scheduler could take a processor back during them, and Winsock was started up again on every connect.
Environment.inheritUpdating and Environment.custom take an EnvMap, which the standard library did not export, so no caller could build the argument. It is public.
A compiler rebuilding itself moved the running binary aside before compiling, so a compile error left the tree with no compiler to build the fix — and the move failed outright when another process, such as a language server, still ran the previous binary. The move happens only once the compile has succeeded, and a previous binary still in use is retired aside rather than deleted.
On Windows, maxon upgrade ran the install script in a Windows PowerShell that inherited the caller’s PSModulePath. Started from pwsh, that names another edition’s modules ahead of this one’s, and the script stopped with The term 'Get-FileHash' is not recognized. The child is handed this PowerShell’s own module directory.

0.2.1 — 2026-09-15

Fixed

The compiler occasionally crashed partway through a build with Range check failed: value outside typealias 'AllocCount'.
A green thread that started reading a socket while another was finishing a read of the same socket could wait forever, unreported by the deadlock detector. It now stops with the documented error for two readers on one socket, every time.
On Windows, a socket receive or send that had already completed when its deadline passed or the socket closed reported a timeout: the bytes received were lost, and a retried send went out twice.

0.2.0 — 2026-09-14

Added

One-line installers for macOS, Linux and Windows, which install the latest release into ~/.maxon.
maxon upgrade, which updates the install the running compiler belongs to.
Container images at ghcr.io/maxon-lang/maxon, in debian and distroless variants for amd64 and arm64.
The Homebrew formula serves x64 and arm64 Linux as well as macOS.
maxon mcp-server, a Model Context Protocol server exposing build, run, test, format, check, IR dumps and error-code lookup to AI tools.

Changed

A green thread that runs for 10 ms without waiting is preempted, including inside a loop that calls nothing, so one busy thread no longer holds up the others.
Socket reads, accepting a connection, subprocess pipes and waiting for a child process park only the green thread that waits; none of them occupies an OS thread any more.
main runs as a green thread whose stack grows as needed, and idle green threads give back stack they no longer use.
Mutating a value that a live let can still observe is refused, however the value was reached — through a call’s result, a closure, an interface method or a union payload as well as a direct field. A write through a method or a field that could reach such a record is a new error, E3159.
Generated code is substantially faster: every function called from one place is inlined, and the optimizer gains value-range analysis, bounds-check elimination against loop limits, loop unswitching, jump threading and hot/cold code layout. fannkuch-redux runs in about 1.2× the time of the C reference, down from 5.4×.
A stack trace names inlined functions as their own frames, and prints up to 100 frames, saying when it stops short.
The compiler runs its per-function optimization passes and instruction selection in parallel.
On Windows, a compiled program’s file description is its own name; the “Built with Maxon” credit is in its Comments field.

Fixed

maxon build intermittently hung on macOS when a build manifest ran subprocesses.
Deep recursion in main overflowed its stack at 1 MB on Windows.
A function returning a tuple of two records could hand back a freed record.
Passing a struct that holds a file or socket to an async call crashed the compiler.
A fault on arm64 macOS with a corrupted stack hung instead of printing a trace, and a fault on a Windows green thread printed its report twice.
maxon run failed in deeply nested directories on Windows.

0.1.1 — 2026-09-10

Added

maxon run, which compiles a program and runs it in one step. A .maxon file may begin with a #! line and be run directly as a script.
maxon help, and maxon help <command> for a single command. Running maxon with no arguments now lists the commands.
--define, which sets a top-level String constant at build time.
Build manifests can declare several named targets, and state the version of what they build.
Compiled executables carry version metadata: a version resource on Windows, a source version on macOS, and a producer string on Linux.

Changed

maxon version replaces the --version and -V flags, and reports the commit and date the compiler was built from.
maxon help replaces the --help and -h flags.
Build.buildOne in a build manifest is renamed Build.build.
maxon fmt separates groups of declarations with one blank line at every nesting depth, not only at the top level.
On Linux and macOS, starting a program that cannot be found raises SubprocessError.executableNotFound instead of spawnFailed.

Fixed

Non-ASCII text displays correctly in a Windows console.
A deadlocked program on Linux reports the deadlock instead of occasionally hanging.
A default parameter value is filled in a global variable’s initializer, not only inside a function.
On Linux, a subprocess started by program name finds the program on PATH, and a file of that name in the working directory is never run in its place.

0.1.0 — 2026-09-08

The first release. One compiler, written in Maxon, that builds itself.

Added

Binaries for x64-windows, x64-linux, arm64-macos and arm64-linux, each built and tested on its own architecture.
A Homebrew formula for macOS.
A VS Code extension, on the Marketplace and Open VSX, with a language server providing diagnostics, hover, go-to-definition, completion, rename, symbols and formatting.
maxon build, fmt, test, spec-test and lsp-server, and a build manifest written as a Maxon program rather than a configuration file.